Primary cell



l. C. BLAKE PRIMARY CELL.

Sept. 30, 1952 Filed May 5 1951 vII/l/ U/azra) "fi*m 36 Patented Sept. 30, 1952 Ivan C. Blake, Freeport, Ill., assign'or to Burgess Batte'y ComDanm-Freeport; III., a corporation' of Delaware 'i Application May 5,1951, ser al No.224684 e This invention relates to' improvements in` primary cells and more particularly to improvements in' the composition off 'dry cells of 'the Leclanch type improved. a

One of the most important problems of the dry cellindustry is the prevention of deterioration of the cells when they are not in operation, that is, while they are in storage or on shelf. There is a tendency for corrosion of the Zinc negative electrode to take place at, the surface thereoi which is exposed to the electrolyte. Frequently this takes place at local areas whereby the negative electrode becomes pitted and prematurely punctured, with the result that the usefullie of the cell and its energy de'lvering capacityare considerably `reduced. Many expedients have been employed to inhibit such objectionable corrosion and among these is the use of chromium trioxide and salts of chromic acid, and also the use of mercury and various salts of mercury; As' an example, the use of the combination of mer'- curic chloride and chromic acid or a soluble salt o'f chromic acid, such as sodium dichromate, is described in U. S. Patent 1,839,498 and has been found to be effective for the purpose. 1 i

In accor dance with the present inventionit has been discovered that a group of double' twosin'gle chromates involved. For convenience they will all be referred to herein as double chromat'es.

It has been found that these compounds when made available at the surface of the negative electrode which is exposed to' the electrolyte possess remarkable efiectiveness in reducing corrosion during inactivity and at the same time exhibit a minimum inhibiting effect upon the current delivering powers of the cell during operation. Exceptionally good results have been,

obtained with barium potassium chromate and it is the preferred compound. v

Accordingly, it is the object of the invention to provide a primary cell of the character. described in which spontaneous' corrosion of the negative electrode is effectively inhibited by the whereby their shelf life is 9 Claims; (CI. 136-407) V inclusion in the cell of a compound from 'the group described heretofore, alone or in combination with asal t of mercury.

I\ by'way 'of illustration and that the invention is not limited'thereto' but may be applied to cells of other structural form. I r

The single figure of the drawing is a midsectionalelevation of the embodiment of the cell. The cell is of flat rectangular shape and is adapted to be-arranged in stacked relation with and connected to additional cells to form a multiple cellbattery of rectangular shape. It comprises'an open-top rectangular container or envelope o of non-conductive electrolyte-resistant material, such as the copolymer of vinyl acetate and vinyl chloride. rubber hydrochloride, a po1ymer of .thylene. orthe like. Within the envelope is the negative electrode 12 which is composed 'of Zinc and is in the orm of a .thin fiat sheet or plate. A terminal conductor !4 is electrically` connected to electrode |2 and projects upwardly therefrom and serves as the negative terminal of the cell. Adjacent to the negative electrode !2 is a separating member !6 which is a sheet or layer of bibulous, non-conductive material such aspaper. Adjacent to the separating member !6 is' a rectangular block of` compressed depolarizing .mix [8, which may be of any' suitable composition, such as a mixture of povvdered manganese dioxide and carbon; -The 'separating member !6 and depolarizing mix l8 are moistened with the cell electrolyte which-may be the usual chlorideelectrolyte composed of a substantiall'ye non-alkaline aqueous solution of zincchloride ductive cap 22 fits tightly upon the upper end of the positive electrode 20 and serves as the positive terminal of the cell.

The envelope o extends above the Separator !6 and the mix l8 and the positive and negative terminals 22 and [4 project above the top of the e envelope n. The space .in the upper portion of the envelope contains a fusible scaling composition 24 composed of pitch or wax. which forms a seal closure for the cell. In practice, the cells which make' up a multiple cell battery are assembled in such manner that they are under pressure and the elements of each cell are held in 3 firm contact with one another. The positive and negative terminals 22 and !4 are exposed above the seal 24 and are available for connection to the other cells cr -an external circuit.

In accordance With the present invention, a double chromate from the group described heretoforejalone or in ccmbination with a mercury salt, is caused 'to' be; present at -the' surface of' the negative e'le'ctrode 12 'which is exposed to the electrolyte; that is, the surface exposed ,to the separating member l. In practice this is done by making the compound accessible to the electrolyte Whereby it goes into solution and is`pre's ent in the electrolyte.

That is ,-:the compound is" brought into access relation ito the electrolytaw This may be acccmplished by direct introduc- 4 Preferably an amount is used which will maintain the electrolyte saturated with the compound 'throughout the life of the cell. Only a relatively e small amount of the compound is required. For

example, in a dry cell of the fiat Construction described heretofore in which the depolarizing mix !3 is 2 inches high, 1% inches wide and inch hick,-andweights 'ts -grams; 'an'amount of bari'u'm potassiumchrom'at containing- CrOs in an amount equal to' approximately 0.085 to 0.30

2; gram has been used with highly satisfactory re- `sults..

This is equivalent to .0025 gram to .012

" gram of CI'Os per square centimeter of negative tion of the compound into the electrolyte during the preparation of the latter, or`by incor-' porating the compound in thedepolarizing mix !8 or the separating member !6 before the cell isgassembled. Any of th s methods ofintroi duction brings. the; compound into;access.relation to the electrolyte and produces ;ubstantially the same results The compounds have-difierent solubilities, but in gencralg--they are soluble -;to

only a limited extent *wa-ter and the aqueous electrolyte, and it is usually-;desrable toincor porate more in thecell' than'wil goinitia'llyinto: solution in the electrolyte. sThepreferredmeth-= od is to incorporate the compound in the mix. 'It becomes dissolved ain'the; electrolyte with which thejmix isr'noistened and therebywbecomes available for' thecinhibitin'g actionzat the .surface of the negative electrode izj v The reasons "for the 'exceptional' efiectivenessiof the double chromate compounds described'is not understoodi The compouhds'are sparingly solub le in water and the electrolyte" aidfgo into solution slowly *The following table gives the amount "of each of the compounds which is dissolved" in water and ina" solution'j compsed of 22w-parts 0f z inc chloride, 28 -parts ot ammoniumchloride and 50 partS'oWatr-,WhCh solution is an eX--'` ample of a suitable' electrolyte. In'each 'case-the grams of the solverit'after standing in the{sol-- vent for '22 hours: i' V Q compound i Water Bariumpotassium chromate Barium sodium chromate Barium ammomum chron ate only-a small quaritit'y ne the om uncifis in solution in the electrolyt atg ny' one' time and' active forthe inhibiting' function; but'this appar'ently is" sufcient; it blieved 'that -as it is electrode surfaceexposed to the electrolyte. This is ,an-excess over'- the amount which will go into solution initially' in' the electrolyte, which is in ,accordance with the explanation given hereto- 'foref' An 'amount greater than given in the foregoing' may' be 'used if desired but generally will not result in improved performance. The amountof the other; double chromate saltsdescribedheretoforemaybe such asto provide an amount of cros generally e quivalent to that set forth ;with respect to bariun i potassium chromate.:

As stated heretoiore, 'mercury may be present irrthe cell pambin t' n .with the double chromate c ompound. The mercury maybe: intro-.

duced inthe .form o fasuitable ;mercury salt having; at least a slight. degree' of solubility in water.

a The salt may beingrganicor Organic in character and the. range of solubilityinay beirom slig htly scluble. to. very s oluble in water: 'or the electrolyte of the celh uitable example of the mercury salt are me urouchloride, mercuric chloride, mercuric broznide tmercurou su1fate,

mercuric. chlorate,'. mercuric nitrate, mercurous ac etate and mercuricacetate. M ercuric nitrate is. very solubleandmeijcurous chloridehas a solu-` bility of ;0002 gram'pe lpO grams of water at 230..: relatively small amountof the mercurysalt isall that, is required For a cell such as has been specifically described heretofore, aquantity containing. mercuryin an amount equal tojapproximately .O0075-to .0l25 gram per cell. crapproximately .000 03 to .0005,gram per squarecen timeter of the zincelectrode:surfaceexposed to perform the inhibitingf unction. Inanypevent, A the mercury salt cont 'bnte ubstantially to thei roved cell is ob-. V

the electrolyte,is satisfactory.

;The mercurysalt maybeircorpcrated in the cell by introducing it directly, into m electrolyte or. it may be incorpratedin the separatingj mem ber ,IG before the 'cell is assembled. f it is iricorporated in theseparating member, ,this may be clone in any ;suitable manner as hytvincludirg.

it in the slurry of papertfibers inthe wetmachine Offa ,paper making apparatusa jdfelting it along with the fibers' uponfgthe paper making' screen. As an alternative the previouslytformedisheet may be moistened withja suspension or solution of the mercury salt and then dred. Inany of these methods of introduction, the mercury .salt is brought into access relation with the electrol'yte and becomes available, at' the' surface of `the negative electrode, apparentl'y by' going into solu.-

ti'o n in the electrolyteg' Even the'slightly soluble i mercury salts, such.`as "mer curous chori'le; are

sufficiently'solubletha't enough becomes available at the 'surface' ofgthenegative electrode to inhibiting acti'onfanjd an il tained by reason ofitsrpresence. V

The folloW hg mroma ndemonstratsthe effectiveness of thedoubl cnromate compounds fj r p dscrihed'lhretofora alone and in electrode exposed to the' electrolyte. Cell No. 1(

contained chromic acidin the electrolyte, which was added in the form of chromium trioxide in the amount of .003 gram' of CrOa. Cell No." 2 contained barium potassium chromate in the mixi'n an amount equivalent to ;0078 gram of CrO. Cell No. 3 contained chromic acid, added in'the form of chromium trioxide, and mercuric chloride in the electrolyte, in amounts equivalent to .00005 gram of Cree and .00005 gram of Hg. This is in accordance with U. S. Patent 1,839,498. Cell No. 4 contained barium potassium chromate in the mix in an amount equivalent to. .0072 gram of CrOz; and mercurous chloride in the electrolyte in an amount equivalent to .000089 gram of Hg;

All had an open circuit voltage' between 1.63 and 1 i 1.66 volts when freshly made, and were tested again after having been on shelf for six weeks. At the second test, any cell which had an open circuit voltage lower than its maximum open circuit voltage minus .04 volt was considered to be defective because experience has shown that such a decline is indicative of rapid deterioration on shelf. The results of the tests are given in Table 2.

Table 2 Number of Number of Cell cells testing cells tested defective No. 1 (CrOa only) 165 54 No. 2 (BaKa(CrO4)2 135 none No. 3 (CrO3+HgClg) 180 14 No. 4 (BaK(CrO4)z+HgCl) 180 I none The very superior inhibiting properties of barium potassium chromate are 'evident from the 'above data. The difference in thelocation of the inhibitor in the various cells produces no apjected to discharge performance tests .after ini Table 3 Capacityi e `noithson shelf. This shows that barium potassium' chromate possesses inhibiting properties superior to those of chromic acid; which is representative of the chromium compounds used prior' 'to this invention.

The data also s'ho'w 'that thc'apaity'of cell No. 4 is' greater than -that of 'any of 'the other cells, which' shows 'that the'addition of` a mer'- cury salt to the barium potassium chromate-:results in improved inhibiting properties.-

Another group of the cells was tested 'for open circit voltage and short circuit current after inactive storage a't"70 F. for a prio'dof-smonths( .The' :data -with e respect to these cells:: are as V 4 follows: i n i Table4 Open Circuit i ShrtCir- Cell' Voltage at cuit Current;`

smonths vatsmonths Volts Amperes 1.584 0.73 1.584 e. 0.77 1.583 0.76 1.599 0.79

the advantages in the use of barium potassium chromate shown by Tables 3 and 4. are due in part at least, to the fact that such compound exerts a lesser current depressing effect than do thechromium compounds used prior to this invention.

active storage for six months at approximately F. The test consisted of discharging batteries composed of a number of the cells connected e in series. Each battery was discharged through a resistance amounting to 166% ohms per cell for a period of four hours and then allowed to rest for 16 hours. This procedure was repeated until the closed circuit voltage of the battery had dropped to the equivalent of 1.0 volt per cell. The Capacity in terms of hours of service on this test for the various batteries is given in Table 3. v

The data show that the capacity of cell No. 2 is greater than that of cell No. 1 after six months Variations may be made from the foregoing specific disclosure by those skilled in the art without departing from the spirit of the present invention. For example, the physical structure of the cell may be vared in any way as desired, the fiat cell illustrated being merely an example of a suitable cell.

What is claimed is:

1. In a primary cell having an electrolyte and a zine negative electrode, a spontaneous corrosion inhibiting compound in access relation to said electrolyte from the group c'onsisting of barium potassium chromate, barium sodium chromate and barium ammonium chromate.

2. In 'a primary cell having a chloride electrolyte and a Zinc negative electrode having a surface thereof exposed 'to said electrolyte, a compound in access relation to said electrolyte V from the group consisting of barium potassium chromate, barium sodium chromate and barium ammonium chromate, said compound being present in an amount providing approximately .0025 to .012 gram of CI'O3 per square centimeter of negative electrode surface exposed to said electrolyte. V

3. A primary cell comprising a positive e1ectrode,` a Zinc negative electrode and' a chloride` 7 r electrolyte, a depolarizing mix in acess rel'ation to said positive electrode, said depolarizing mix containing a compound from the group consisting of barium potassium chromate, barium sodium chromate and barium ammon'um chromate. a I

4. In' a primary cell having a chloride electrolyte and a zinc negative electrode, barium potassium chromate in access relation to said'electrolyte. r .u v i 5.. In a primary cell havingva chloride electrolyte' and a zine negative electrode, a mercury salt having ati least.. a slight degree of solubility in Water and a double chromate compound'from the group ;consistin'g of .barium potassium chromate, barium sodium chrom'ate and barium'ammonium chromatein access-relation to said eleci tro1yte. i v V 6. In a primary' cell having anelectrolyte and a zincnegative"electrode, having a' surface thereofexpose'd tosaid electrolyte, a mercury 'salt having at leasta slight degree ofsolubility in water and adoublechromate compound from the group sodium chromate and barium ammonium chromate in 'access relation to said e1ectro1yte,`said mercury salt and double chromate compound consistingof barium potassium chromate, barium respectively being present in amounts providing approximately .00003 to .0005 gram of mercury and approximately .0025 to .012 gram of CI'Os per square centimeter of zine electrode surface ex posed to said electrolyte.

. 7. In a primary cell ;having a chloride electrolyte and a' Zinc negative` electrode havingna' surface thereof exposed to said electrolyte, bar-z ium potassium chromate and a mercury salt'having at least a slight degreeof solubility in water in access relation with said electrolyte said chromate and said' mercury salt being present respectively amounts providing approximately .0025130 .012' gram 'of CrOa and approximately .00003 to ;0005 gram of mercury per square centimeter of zine electrode surface exposed to' said electrolyte r 8. In a primary cell. havinga chloride electrolyte and a zince negative electrode, barium sodium chromate in access relation to said electrolyte'. 1 r 9:'1'1'1 a primary cell having a chloride e1ec:-, trolyte and a zine negative electrode, barium ammonium chromate in access relation to said' electrolyte. i

,- v s IVAN C.

REFERENCES CITED i The following references are of recordin the file of this patentr i UNITED STATES PATENTS Number Name Date 1,839,498 Porth Jan. 5, 1932 1421045 Ruben i June 10, 1947 2,491,640 Blake Dec. 20, 1949 

1. IN A PRIMARY CELL HAVING AN ELECTROLYTE AND A ZINC NEGATIVE ELECTRODE, A SPONTANEOUS CORROSION INHIBITING COMPOUND IN ACCESS RELATION OF SAID ELECTROYLTE FROM THE GROUP CONSISTING OF BARIUM POTASSIUM CHROMATE, BARIUM SODIUM CHROMATE AND BARIUM AMMONIUM CHROMATE. 